Field of the Invention
The present invention relates to the general technical field of agricultural machinery and in particular power seed drills. The invention more specifically concerns a declutching device for a seed distribution unit in a power seed drill.
A power seed drill includes a hopper and a plurality of distribution elements as described below. The distribution elements are arranged at the lower output of the hopper and are fed with seeds from the hopper by gravity. Each distribution element measures out the seeds before they are conveyed to a corresponding row or furrow.
Discussion of the Background
It is known that to meet a plant's needs during its growth and ensure a good yield from the field, cultivation operations involving fertilisation and plant health treatments are required after sowing. These different operations are carried out in accordance with the maturity of the plants. During sowing, the field is tramlined, i.e. parallel unsown tracks used as markers for the fertilisation and/or treatment devices are provided in the field. The tramlining is carried out by the declutching or clutching of some distribution elements. The intervals between the unsown tracks (known as tramlines) and their width are determined based on the tracks of the tractors, seeds and treatment devices, the width of the wheels of the latter and a ratio determining the width between the seed drill and the treatment devices. Cutting off the distribution to show the tracks of the treatment device prevents the plants situated in the path of the treatment device being crushed, therefore preventing seed waste.
A known distribution element 31 is shown in FIG. 2. This distribution element is arranged at the hopper lower output. Such a distribution element 31 includes a frame 36 that defines an inlet chamber for the seeds 37 ahead of and above a movable section 39 and an outlet chamber for the seeds 38 further down from and below the section 39.
The distribution element 31 also includes a hub 40, a gearwheel 41, a grooved wheel 42 and a clutching spring 43 (FIG. 2).
The hub 40 has a longitudinal body 40a and a radial ring 40b at one end of the body 40a. 
The hub 40 is attached to a drive shaft 44 of the seed drill by a peg 45.
The gearwheel 41 is arranged around the hub 40.
In detail, the gearwheel 41 includes a longitudinal section 41a and a ring 41b. An annular recess 41c is provided where the sections 41a and 41b meet. A notch 41d is also provided across the section 41a. 
The ring 41b has teeth 48. Each of these teeth 48 in this embodiment includes a radial surface 48a opposite a tilted surface 48b. The successive surfaces 48a and 48b are connected, on the one hand, by a top surface 48c and, on the other hand, by a bottom surface 48d (see FIG. 1 or 3a).
The gearwheel 41 is arranged concentrically around the hub 40 and the ring 40b is housed in the recess 41c (FIG. 1).
The wheel 42 includes helical splines in the embodiment shown. The splines can also be straight. Other known wheels include lugs rather than splines. In FIG. 2, the wheel 42 is attached to a block 34. An assembly including the block 34, the hub 40, the gearwheel 41 and the wheel 42 can move along a given sliding range relative to the frame 36 to adapt the spline length to the desired seed flow at the output.
A valve 35 is provided opposite the wheel 42 to adapt the distribution to the dimension of the chosen seeds (FIG. 2).
The wheel 42 has a main body 42a with splines on its outer surface and a tubular portion 42b extending longitudinally inside the body 42a. 
The clutching spring 43 is helical. It includes two series of coils 43a and 43b and in this case a plurality of welded coils 43c. There are two welded coils 43c in this case, although there may be three or more. Welding the coils 43c prevents them from sliding between the hub 40 and the tubular portion 42b. 
The spring 43 also includes a first lug 43d and a second lug 43e, which in this case extend longitudinally opposite each other from the first and second series of coils 43a and 43b. 
The first lug 43d of the spring is housed in the notch 41d of the gearwheel 41 in order to keep the spring 43 and the wheel 41 together during rotation.
The second lug 43e comes into contact with a finger (not shown) of the wheel 42, protruding between the body 42a and the tubular portion 42b. 
During seeding, the shaft 44 drives the hub 40 in rotation and drives the spring 43 by friction, the first lug 43d driving the gearwheel 41. As shown in FIG. 1, the elements 40, 41, 43 and 44 revolve in the anti-clockwise direction R. The clutching spring 43 tightens around the body 40a and the tubular portion 42b, driving the wheel 42 in rotation. The distribution element 31 is then clutched and distributes the seeds. The angular speed of the drive shaft 44 depends on input parameters such as the tractor's speed and the previously chosen gear of a gearbox linked to the shaft 44.
The distribution element 31 can also be declutched using a declutching lever 10 (FIG. 1).
The lever 10 includes a body 20, a bolt 25, a spring 26 and a buffer 27.
The body 20 of the lever 10 has first hooks 21 via which it is mounted by a pivot connection around a fixed pivot rod 15 relative to a chassis (not shown) of the seed drill. The body 20 also has second hooks 22a and 22b via which it is attached to a selection bar 16, which is here square shaped. The purpose of the bar 16 is to move the lever 10 around the rod 15 between two end positions: a retracted position and a deployed position.
The body 20 also has a tongue 23 provided with a transverse and flat edge 24 at its distal end.
The bolt 25 includes a screw 25a and a lock nut 25b. The spring 26 is a helical compression spring, for example with flat ends, i.e. arranged in a plane.
The buffer 27 is in the shape of a plate with an opening (not shown) for screws to pass in its centre.
The lever 10 is shown here with the buffer 27 mounted flat on the edge 24. More specifically, the buffer 27 is held on the edge 24 by the bolt 25 and the spring 26, such that the spring 26, the edge 24 and the lower part of the buffer 27 are kept in this order between the nut 25b and the screw head 25a. The buffer 27 has a head 28 of a larger width than the sliding range of the wheel 42 relative to the frame 36.
When the buffer 27 is mounted on the lever 10, the latter is able to declutch the distribution element 31. Indeed, when the lever 10 is in a deployed position, a head of the buffer 27 (FIG. 1) is housed between two successive teeth 48. The wheel 41 is blocked from rotating by the buffer 27. The lug 43d is prevented from turning by the wheel 41, the spring 43 is loosened and the driving of the wheel 42 by the shaft 44 is disengaged. The distribution element 31 is then declutched and the seed distribution stops.
The spring 26 provides elasticity in the event that the buffer 27 strikes one of the surfaces 48b or 48c when the lever 10 is moved into the deployed position.
According to the tractor's position in the field during sowing, the bar 16 moves the lever 10 and its buffer 27 between the retracted and deployed positions as necessary. Prior to seeding, a buffer 27 is only provided on the levers 10 opposite the elements 31 that will be declutched.
Positioning the levers, moving them between distribution elements or withdrawing them requires intervention with the use of tools before each seeding. Furthermore, the available space within seed drills is restricted. Handling and adjusting the buffers is therefore awkward. The restricted space also increases the risk of dropping parts or tools into the machine during work, which wastes time.